Some circuit board manufacturers occasionally have the need to remove soldered lead frame integrated circuit (IC) components from circuit boards. For example, a circuit board manufacturer may have inadvertently manufactured a batch of circuit boards with the wrong, faulty or unreliable (e.g., xe2x80x9cout of specxe2x80x9d) lead frame components. Rather than scrap the otherwise correctly manufactured circuit boards, the manufacturer unsolders the original lead frame components from the circuit boards, cleans the circuit boards, and subsequently solders new lead frame components to the circuit boards.
A typical lead frame component is rectangular in shape and has sets of metallic leads that extend on two sides (i.e., opposite sides), or alternatively on all four sides. After such a component has been soldered to a circuit board, a circuit board manufacturer can unsolder that component from the circuit board using a manifold assembly that blows heated gas (e.g., heated nitrogen gas) therethrough. To this end, a user (e.g., a trained technician employed by the circuit board manufacturer) typically places the circuit board on a flat heater so that the side of the circuit board having the lead frame component faces up. The flat heater raises the overall temperature of the circuit board (e.g., to a temperature of 100 degrees Celsius). The user then lowers the manifold assembly over (i.e., on top of) the lead frame component. The manifold assembly typically includes a set of metallic exhaust elements which extend from a central location down over the metallic leads of the lead frame component. Typically, the manifold assembly further includes a vacuum element which is disposed between the exhaust elements and which extends from the central location down on top of the package of the lead frame component. After the user lowers the manifold assembly over the lead frame component, the user activates (i) a vacuum source that sucks air through the vacuum element, and (ii) a heated gas source that blows heated gas through the exhaust elements. The exhaust elements of the manifold assembly direct the heated gas in a downward direction toward the circuit board surface and over the metallic leads of the component. Eventually, the heated gas melts the solder holding the metallic leads of the component thus freeing the component from the circuit board. The vacuum element takes hold of the lead frame component, and the user then lifts manifold assembly and the component (which is now attached thereto) away from the circuit board thus completing removal of the component.
In subsequent steps, the manufacturer cleans the circuit board and prepares the circuit board to receive a new lead frame component. To this end, the user typically removes (e.g., melts and vacuums) any remaining solder from the exposed mounting location of the circuit board (i.e., the circuit board location on which the original lead frame component resided), and washes the mounting location using a special solution that removes oxidized metal and any remaining contaminants.
Next, the user installs the new lead frame component on the mounting location of the original lead frame component. To this end, the user distributes, or xe2x80x9cprintsxe2x80x9d, solder paste over the mounting location using a stencil. Next, the user positions the new lead frame component over the mounting location using a workstation having a microscope and a set of gears that enable the user to locate the new lead frame component over the mounting location with high precision. The user then applies heat to solder the new lead frame component in place. In some situations, the user can use the same flat heater and manifold assembly which were used to remove the original lead frame component (e.g., the flat heater and the manifold assembly can be integrated parts of the workstation). In other situations, the user employs other devices to solder the new lead frame component in place (e.g., automated equipment).
Some circuit board manufacturers can remove and install ball grid array (BGA) components using a metallic nozzle that blows heated gas over the BGA components in order to heat the BGA components in a top down manner. That is, the nozzle blows heated gas onto the top of the BGA component toward the surface of the circuit board. Accordingly, the temperature of the top of the BGA component gradually rises ahead of the temperature at the bottom of the BGA component, and eventually the heat permeates to the soldering region underneath the BGA component. Accordingly, the temperature of the soldering region of the BGA component (i.e., an array of solder balls) eventually exceeds the solder melting temperature and the BGA component becomes free. A central vacuum element in the middle of the nozzle grabs the BGA component in a manner similar to that for the lead frame devices so that the BGA component can be removed from the circuit board by lifting the nozzle away from the circuit board.
After the BGA component is removed, the mounting location of the circuit board can be cleaned of old solder and printed with new solder for installation of a new BGA component. Then, the user can install the new BGA component onto the mounting location. In some situations, the user can use a workstation that employs the same metallic nozzle which was used to remove the BGA component. In other situations, the user can employ automated equipment to install the new BGA component. A typical amount of time for the entire process of removing an old BGA component, cleaning and prepping the mounting location, and installing a new BGA component is approximately one hour.
Unfortunately, there are deficiencies to above-described conventional approaches to removing circuit board components. For example, it takes a significant amount of time to remove a BGA component from a circuit board and install a new one (e.g., one hour). In situations that require removal and replacement of such a component from many circuit boards (e.g., mass production situations), the component removal/installation station that performs the process of removing the old circuit board components and installing new circuit board components in their place can easily become a bottleneck.
Additionally, the process of installing a new BGA component using the above-described top down heating approach can provide significant stresses on the component and the mounting location of the circuit board. In particular, the uneven heating of the component and the mounting location for an extended period of time (i.e., raising the temperature of the top of the component ahead of the component underside and the mounting location of the circuit board) provides substantial thermal stresses that raise reliability concerns. That is, severe distortions (e.g., twisting and bending) in the component and in the circuit board can damage any of the interconnects between the silicon chip and the internal conductors of the circuit board, the circuit board laminate and/or the neighboring interfacial vias (e.g., fracturing a wire bond).
Furthermore, the above-described conventional manifold assembly, which has the exhaust elements and the vacuum element, is not well-suited for removing or installing a circuit board component having a solder region hidden between the component itself and the circuit board since the manifold assembly is typically lowered on top of an component, the exhaust elements of the manifold assembly typically blow heated gas toward in a downward direction toward the circuit board surface. The heated gas typically does not blow underneath the IC component but simply down on top of the metallic leads.
In contrast to the above-described conventional approaches to removing and installing circuit board components, the invention is directed to techniques for modifying a circuit board (e.g., removing and/or installing a circuit board component) by providing fluid (e.g., heat gas) between the circuit board component and the circuit board. As such, the temperature of the circuit board and the component can be controlled in a more even manner (e.g., the temperature on the top and the bottom of the component can be raised simultaneously) relative to the above-described conventional top down manner. Accordingly, for a component having a soldering region between the component and the circuit board (e.g., a BGA component), the thermal stress placed on the component and the circuit board mounting location can be minimized. Additionally, the temperature of the soldering region between the component and the circuit board can be raised more quickly than in the conventional approaches thus shortening the time required to remove an old component and install a new one to improve the manufacturing process throughput (e.g., to reduce the total time required to completely rework a circuit board).
One arrangement of the invention is directed to a nozzle for applying fluid (e.g., a heated gas) to a solder region of a circuit board component. The circuit board component has a set of fluid-delivery edges and a set of fluid-escape edges. The nozzle includes a top member to connect with a fluid source, and a set of fluid-delivery side members coupled to the top member. Each fluid-delivery side member extends from the top member and around a respective fluid-delivery edge of the circuit board component when the circuit board component engages with the nozzle. Each fluid-delivery side member defines (i) at least a portion of a fluid-delivery channel that extends from a vicinity adjacent the top member toward the solder region of the circuit board component when the circuit board component engages with the nozzle, and (ii) a barrier that substantially prevents fluid from escaping from the solder region of the circuit board component along the respective fluid-delivery edge for that fluid-delivery side member. Accordingly, flow can be forced underneath the component in order to melt solder at the soldering region in order to quickly unsolder the component from the circuit board or solder the component to the circuit board. This arrangement is simpler, requires less time, and does not compromise reliability as compared to the earlier-described conventional top down heating approach.
In one arrangement, the nozzle further includes a set of fluid-escape side members coupled to the top member. Each fluid-escape side member extends from the top member and around a respective fluid-escape edge of the circuit board component when the circuit board component engages with the nozzle. Each fluid-escape side member defines at least a portion of a fluid-escape channel to enable gas to escape from the solder region of the circuit board component when the circuit board component engages with the nozzle and when the set of fluid-delivery side members contact the circuit board. Accordingly, fluid (e.g., heated gas) escapes through the fluid-escape channels thus providing a path for constant fluid flow for enhanced heat delivery to the solder region of the circuit board component.
In one arrangement, the set of fluid-escape side members couple to the set of fluid-delivery side members. In this arrangement, the top member, the set of fluid-delivery side members and the set of fluid-escape side members form a cavity over a side of the circuit board component that is opposite the solder region (i.e., over the top of the component) when the circuit board component engages with the nozzle. As such, fluid flowing through the cavity can quickly bring the side of the circuit board component that is opposite the solder region to the same temperature as the solder region thus avoiding thermally stressing the circuit board component with substantially uneven temperatures.
In one arrangement, the set of fluid-delivery side members includes exactly two fluid-delivery side members, and wherein the set of fluid-escape side members includes exactly two fluid-escape side members. In this arrangement, the two fluid-delivery side members and the two fluid-escape side members can form a rectangle. Preferably, the two fluid-delivery side members are disposed on opposite sides of the rectangle, and the two fluid-escape side members are disposed on other opposite sides of the rectangle.
In one arrangement, each fluid-escape side member includes an interference portion which defines an interference surface that prevents the circuit board component from contacting the top member when the circuit board component engages with the nozzle. In this arrangement, the interference portion of each fluid-escape side member further can define at least one vacuum channel or hole through the interference surface to hold the circuit board component in response to a vacuum from a vacuum source. Accordingly, the nozzle can hold the circuit board component along its periphery and thus avoiding the need for a central vacuum element.
The features of the invention, as described above, may be employed in manufacturing systems, devices and methods such as those of EMC Corporation of Hopkinton, Mass.